Electrostatic chucks are devices which have gained wide usage in the semiconductor field for clamping semiconductor wafers during manufacturing processes. These chucks eliminate the need for mechanical clamping mechanisms, which are often clumsy and induce contamination into the processing chambers. Typical electrostatic chucks utilized in the prior art can be found in U.S. Pat. Nos. 4,184,188 (Briglia); 4,384,918 (Abe); 4,724,510 (Wicker, et al.); and 4,665,463 (Ward, et al.).
Briglia discloses an electrostatic clamp having interdigitated, polarized electrodes disposed between layers of silicone rubber and supported by an aluminum plate which is attached to a water cooled base. The wafer under process sits on top of a layer of silicone rubber and is clamped by the electromagnetic field generated by the underlying electrodes. Briglia also discloses an alternative embodiment wherein aluminum electrodes are deposited onto an alumina support and insulated by oxidation. The electrode structure is secured "both mechanically and with good thermal conductivity" by a "water cooled plate".
Abe discloses an electrostatic chuck wherein aluminum clamping electrodes are insulated by either polytetrafluorethylene, polyethylene or silicon gum. The electrodes are, in turn supported by a water cooled support base, or a heated support base.
Wicker, et al. discloses an electrostatic chuck wherein the clamping electrodes are deposited on a semiconductor wafer and insulated by a layer of either CVD oxide, polyimide, or a suitable glass. The clamp is supported by "conductive support".
Ward, et al. discloses an electrostatic chuck wherein a center, circular clamping electrode is insulated by a layer of epoxy resin, such as Araldite loaded with particulate alumina or mica. The center electrode also serves as the heat sink for the wafer in process.
All of the above mentioned electrostatic chucks have insulated electrodes supported by an undefined cooling "support". A problem exists with these chucks and other known electrostatic chucks, however, in that the materials utilized for the electrical insulators have radically different thermal expansion characteristics than the materials utilized for the cooling supports. Therefore, subjecting these chucks to widely varying temperature cycles causes separation between the dissimilar materials. As a result, the chucks can only be utilized in very narrow temperature ranges, thereby limiting the application of each chuck to selective manufacturing processes. Even with this limitation, the chucks suffer from short lifetimes, low reliability and high costs. These problems are amplified because the chucks are a major cause of "down time" on the manufacturing line.
An electrostatic chuck which overcomes the above mentioned deficiencies is therefore, highly desirable.